This invention relates to a releasable connector arranged to be inserted between coiled tubing, a pipe string or similar tubular string and a tool/piece of equipment, and arranged to release and be divided into two sleeve-shaped interconnectable parts, of which one is connected to the coiled tubing, and the other is connected to said tool/equipment, and in which the two sleeve-shaped parts of the connector are held together in a blocked non-released position by means of a locking device which is kept in its locked position by means of a retaining sleeve, which is axially displaceable on release, or the initial release, of the connector, said retaining sleeve releasing said locking device by a sufficient axial displacing movement, said locking device thereby initiating the release, said connector comprising internally a coaxial displaceable piston body with a transversal end surface, which can be actuated by fluid pressure in order to start the release process, and which influences, when being displaced, the locking device to release its locking effect and allow division of the connector into said two interconnectable parts.
When released intentionally, the connector is divided between its connecting ends, whereby the coiled tubing etc. is separated from the downhole tool.
Such connectors are generally known in several embodiments, and are brought to function, i.e. brought to release, should, for example, the downhole tool jam and become stuck and resist withdrawal together with the coiled tubing/pipe string and the connector in undivided condition.
An example of a connector of this kind is disclosed in NO 180.552. The releasable locking means holding together two separable parts of the connector, here consists of a radially expandable locking ring, which is in a compressed, non-expanded condition in its locking position, blocking the two separable parts of the connector. In its locking position, the locking ring engages a lock mandrel included in the connector, and is surrounded by an axially displaceable retaining sleeve, which is shear-pinned in a non-displaceable position in the active position of the connector. Whenever it is desirable to release the connector for division into an upstream part, which may be extracted together with intact coiled tubing (pipe string), and a downstream part, which will remain in its position downhole together with the tool, an internal seat formed in a piston sleeve is used in a well-known manner, whereby a ball is released from a surface position to settle sealingly on the seat, after which drilling mud/drilling fluid or other fluid is pumped down under pressure from the surface to exert a considerable pressure on the reaction surface of the piston sleeve opposite the pressure, consisting of the ball surface of the ball and the seat surface opposite the direction of flow of the pressure fluid. By a certain pressure build-up upstream of the ball-/sphere-like sealing body cooperating with the seat of the piston sleeve, the piston sleeve is put into a displacing movement, whereby said retaining sleeve is subjected to an axial compressive force. The shear pins are sized to shear by for example the compressive force (e.g. equalling 70.3 kg/cm2xe2x80x941000 psi) achieved thereby. When the shear pins have been shorn, the piston sleeve and thereby the retaining sleeve are displaced until the latter is no longer surrounding the locking ring, but releases it. In its released condition the locking ring expands and releases the connector.
This known connector can release on unintentional pressure build-up inside the connector.
Unintentional pressure build-up, which may make the connector release, may occur during so-called underbalanced perforation. The formation pressure is lower than the hydrostatic pressure of the well before perforation.
A hydraulically releasable connector of the kind initially mentioned, is known from the Norwegian patent document No. 305.715. This known connector is arranged for the releasable connection of a tool to the end of coiled tubing. The casing of the connector is formed with two or more hydraulic channels for the transfer of hydraulic fluid from hydraulic lines run through the coiled tubing to said tool. The connector is retained in its connected position by means of a locking device which is secured by means of an axially displaceable sleeve, which again is retained in its securing position by means of transversal shear pins. The retaining sleeve is arranged as a piston-like hydraulically manoeuvrable means, and is provided with annular seals of different sealing diameters. These seals define annular areas on the piston-like retaining sleeve, and these piston areas each have a hydraulic channel arranged thereto. The retaining sleeve is subjected to an axial force, equalling the sum of the product of the pressure in each of the hydraulic channels and the respective annular piston area. The shear pins are sized to be brought to break, whenever both annular piston areas are subjected to hydraulic working pressure. This connector also has not got any delaying means (such as a spring and/or viscous liquid) on the underside of the piston-like retaining sleeve.
Thus, the object of this invention has been to arrange it so that a brief pressure increase inside the connector will not necessarily result in full release and division of the connector into two separate parts.
The object is realized, according to the invention, by means of a connector of the kind specified in the introductory part of Claim 1, which distinguishes itself through the features appearing from the characterizing part of Claim 1.
On undesirable pressure build-up in the connector, the return spring of the piston may be compressed somewhat, and the shear pin(s) may shear, but the release-delaying device according to the invention prevents the complete compression of the return spring, which is necessary for the release of the locking mechanism.
The release-delaying device consists of a spring chamber filled with lubricating grease, in which the piston forces, during its displacement and compression of the spring, the lubricating grease (or other particularly viscous liquid or pumpable substance) out through a choked opening, preferably adjustable in size, which resists accelerated rate of extrusion, thus delaying the displacement of the piston, and thereby the compression of the spring, for a period of time, during which the locking ring or other locking mechanism still has not been brought completely out of its locking position when the unintentional pressure increase ceases. When all of the lubricating grease/liquid has been forced out of the spring chamber, the delaying means has been spent, whereby there is nothing else but the return spring attempting to hold back the piston. If the compressive force, acting axially on the piston, exceeds the counter-force of the spring, the piston is displaced during the compression of the spring, and completes its stroke to release the locking ring/mechanism.
If it is desired to release the connector intentionally and consciously, the reaction surface of the piston is exposed to high pressure, e.g. 70.3 kg/cm2(1000 psi), for a period of time, which is known, from experience, to exceed the time for the forcing out of the lubricating grease from the spring chamber.